/****************************************************************************/
/*                                                                          */
/*       SERIAL.C:  Interrupt Controlled Serial Interface for RTX-51        */
/*                                                                          */
/****************************************************************************/

#pragma CODE DEBUG OBJECTEXTEND

#include <reg52.h>                    /* special function register 8052     */
#include <rtx51.h>                    /* RTX-51 functions & defines         */

#define  OLEN  8                      /* size of serial transmission buffer */
unsigned char  ostart;                /* transmission buffer start index    */
unsigned char  oend;                  /* transmission buffer end index      */
idata    char  outbuf[OLEN];          /* storage for transmission buffer    */
unsigned char  otask = 0xff;          /* task number of output task         */

#define  ILEN  8                      /* size of serial receiving buffer    */
unsigned char  istart;                /* receiving buffer start index       */
unsigned char  iend;                  /* receiving buffer end index         */
idata    char  inbuf[ILEN];           /* storage for receiving buffer       */
unsigned char  itask = 0xff;          /* task number of output task         */

#define   CTRL_Q  0x11                /* Control+Q character code           */
#define   CTRL_S  0x13                /* Control+S character code           */

bit   sendfull;                       /* flag: marks transmit buffer full   */
bit   sendactive;                     /* flag: marks transmitter active     */
bit   sendstop;                       /* flag: marks XOFF character         */

/****************************************************************************/
/*       putbuf:  write a character to SBUF or transmission buffer          */
/****************************************************************************/
putbuf (char c)  {
  if (!sendfull)  {                   /* transmit only if buffer not full   */
    if (!sendactive && !sendstop)  {  /* if transmitter not active:         */
      sendactive = 1;                 /* transfer the first character direct*/
      SBUF = c;                       /* to SBUF to start transmission      */
    }
    else  {                           /* otherwize:                         */
      outbuf[oend++ & (OLEN-1)] = c;  /* transfer char to transmission buffr*/
      if (((oend ^ ostart) & (OLEN-1)) == 0)  sendfull = 1;
    }                                 /* set flag if buffer is full         */
  }
}


/****************************************************************************/
/*       putchar:  interrupt controlled putchar function                    */
/****************************************************************************/
char putchar (char c)  {
  if (c == '\n')  {                   /* expand new line character:         */
    while (sendfull)  {               /* wait for transmission buffer empty */
      otask = os_running_task_id ();  /* set output task number             */
      os_wait (K_SIG, 0, 0);          /* RTX-51 call: wait for signal       */
      otask = 0xff;                   /* clear output task number           */
    }
    putbuf (0x0D);                    /* send CR before LF for <new line>   */
  }
  while (sendfull)  {                 /* wait for transmission buffer empty */
    otask = os_running_task_id ();    /* set output task number             */
    os_wait (K_SIG, 0, 0);            /* RTX-51 call: wait for signal       */
    otask = 0xff;                     /* clear output task number           */
  }
  putbuf (c);                         /* send character                     */
  return (c);                         /* return character: ANSI requirement */
}


/****************************************************************************/
/*       _getkey:  interrupt controlled _getkey                             */
/****************************************************************************/
char _getkey (void)  {
  while  (iend == istart)  {
    itask = os_running_task_id ();    /* set input task number              */
    os_wait (K_SIG, 0, 0);            /* RTX-51 call: wait for signal       */
    itask = 0xff;                     /* clear input task number            */
  }
  return (inbuf[istart++ & (ILEN-1)]);
}


/****************************************************************************/
/*       serial:  serial receiver / transmitter interrupt                   */
/****************************************************************************/
serial () interrupt 4 using 1  {     /* use registerbank 1 for interrupt    */
  unsigned char c;
  bit   start_trans = 0;

  if (RI)  {                         /* if receiver interrupt               */
    c = SBUF;                        /* read character                      */
    RI = 0;                          /* clear interrupt request flag        */
    switch (c)  {                    /* process character                   */
      case CTRL_S:
        sendstop = 1;                /* if Control+S stop transmission      */
        break;

      case CTRL_Q:
        start_trans = sendstop;      /* if Control+Q start transmission     */
        sendstop = 0;
        break;

      default:                       /* read all other characters into inbuf*/
        if (istart + ILEN != iend)  {
          inbuf[iend++ & (ILEN-1)] = c;
        }
                                     /* if task waiting: signal ready       */
        if (itask != 0xFF) isr_send_signal (itask);
        break;
    }
  }

  if (TI || start_trans)  {          /* if transmitter interrupt            */
    TI = 0;                          /* clear interrupt request flag        */
    if (ostart != oend)  {           /* if characters in buffer and         */
      if (!sendstop)  {              /* if not Control+S received           */
        SBUF = outbuf[ostart++ & (OLEN-1)];      /* transmit character      */
        sendfull = 0;                /* clear 'sendfull' flag               */
                                     /* if task waiting: signal ready       */
        if (otask != 0xFF)  isr_send_signal (otask);
      }
    }
    else sendactive = 0;             /* if all transmitted clear 'sendactive*/
  }

}


/****************************************************************************/
/*       serial_init: initialize serial interface                           */
/****************************************************************************/
serial_init ()  {
  SCON  = 0x50;                      /* mode 1: 8-bit UART, enable receiver */
  TMOD |= 0x20;                      /* timer 1 mode 2: 8-Bit reload        */
  TH1   = 0xf3;                      /* reload value 2400 baud              */
  TR1   = 1;                         /* timer 1 run                         */
  os_enable_isr (4);                 /* enable serial port interrupt        */
}
